The long-term goal of our research program is to understand the biochemical processes which control differentiation of erythroid cells. Our method of approach has been to analyze various properties of a permanent Friend Leukemia Virus-transformed erythroleukemic cell line which exhibits a characteristic erythroid differentiation when cultured in vitro under appropriate conditions. One part of our work concerns what controls are exerted in these cells during differentiation on the transcription, processing and translation of globin messenger RNA. The properties of globin mRNA sequences present in the nucleus and cytoplasm are being examined. Globin mRNA sequences are assayed by DNA-RNA hybridization with a DNA copy of globin mRNA synthesized with RNA dependent DNA polymerase. We plan to complement our studies with whole cells by experiments designed to study the transcription and processing of globin mRNA sequences in cell-free extracts. The other major area of investigation involves the use of cellular genetics for analyzing the regulatory processes controlling erythroid differentiation. The properties of cell hybrids formed between erythroleukemic cells and other mouse and human cell lines are being examined in order to: a) determine the biochemical basis of extinction of differentiated functions in somatic cell hybrids, and b) assign the human loci specifying globin chains to particular human chromosomes. A second approach has been to isolate mutant erythroleukemic cells which are unable to differentiate. At present we have several mutant cell lines deficient in their ability to produce hemoglobin. These mutants are being analyzed biochemically for the presence of several phenotypic markers of erythroid differentiation and studied further by complementation analysis using cell hybrids formed between mutants and parental cells and amongst mutants.